As is well known, the tapering of the mould passage serves to compensate for the shrinkage of the cast strand that takes place within the mould during the solidification process. The production of this tapering is particularly problematic with large sized double T-shaped preliminary sections or beam blank sections because the latter are essentially produced from a tubular semi-finished product by forming, and because such sections have very large dimensions which can be over 800 mm total width, over 400 mm flange width and over 120 mm bar thickness. Since casting is slower with such large sizes than with smaller sizes, one requires for them a relatively large degree of tapering in the mould. However, in conventional moulds this tapering can only be produced to a limited extent because it is well known that the mould passage of the latter is produced during forming by means of a punch which is drawn as a female mould through a tubular blank or semi-finished product. Therefore, according to the known production method one can not in any case produce tapering towards the centre of the mould with the lateral inner sides of the profile because it is simply not possible to change the cross-section of the female mould used.